Aircraft brakes operate differently under dry and wet conditions because the frictional surfaces of the brake discs have one coefficient of friction in the dry condition and a lower coefficient of friction in the wet condition. To compensate for this reduction in the coefficient of friction in the wet condition, the pressure forcing the discs together must be increased. It has been found that a large difference in the required braking pressure between the wet and dry braking condition is undesirable for two reasons. First, the greater the difference in required braking pressure the more difficult it is to control the application of the lower braking pressures in the dry operating condition. Too much pressure applied in the dry braking condition causes the brake to lock the wheel and results in a loss in braking efficiency. Second, where substantially greater pressures are necessary in the wet braking condition the fluid cylinder and piston assemblies must be enlarged and the entire wheel and brake assembly must be of stronger, heavier construction to withstand the greater stresses. This results in a larger brake construction which is not desirable for aircraft where the weight and space limitations are critical.